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Hosted by the Space Frontier Foundation to assist the National Security Space Office study on Space-Based Solar Power development.

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Anything you say here may influence the security space community to advance space-based solar power technologies like low cost launch systems, wireless power transmission, on-orbit construction, and extraterrestrial resource development that are needed to harvest endless clean energy from space.

Technical Discussion On Power Beaming: Engineers Take Note!

Regarding power beaming from satellites at GEO to the Earth’s surface:

“The atmosphere has two bandwidth width windows though which it is possible to beam power between space and the surface efficiently, and outside of which atmospheric absorption will kill you: (1) a microwave window, of which the 2.45 GHz frequency (~ 12 centimeter wavelength) employed in the 1970s DoD/NASA reference SPS design is typical, and (2) a visible window extending perhaps as far into the near infrared as a micron of so in wavelength. …

The microwave window allows radio astronomers to see galaxies with their large antennae at the Earth’s surface; the second allows us to see the stars with our eyeballs. However, the wavelengths of these windows differ by a factor of 100,000, with profound implications for sizing of power beamers for space solar power applications. A major consequence of the beam spreading by diffraction related to that employed by Arthur Smith below — that is, the factor X = (transmitter aperture)x(receiver aperture)/(wavelength)(distance) must be of order one for the transmission efficiency to be of order one or greater because only then will the receiver aperture be big enough to capture the beam main lobe — is that kilometer or greater sized transmitting and receiving apertures are needed for microwave beamers to capture the main fraction of transmitted power from geostationary orbit (GEO) — the best location at least near term of a solar power satellite.

The diffraction limit on electromegnetic waves is a fundamental law of physics built into the structure of this universe. It can’t be beaten by clever engineering, and not for lack of trying (sparce arrays, etc.) The DoE/NASA reference SPS design of the 70s wound up with a 1 kilometer phased array transmitter and 10 x 13 kilometer rectenna. With these dimensions, and in order to attain a reasonable intensities inside the main lobe of the beam, you need a gigawatt sized SSP; with 5 x 10 kilometer solar panel arrays: ten gigawatts for Peter Glaser’s DoE/NASA reference design; perhaps as little as one GW for John Mankins’ Fresh Look Study cleverly designed technology. But still big. Meaning big capital investment prior to first power. In all fairness, fusion with its different physics scaling laws, also drives you for different reasons to large machines, like the 12 billion dollar International Experimental Thermonuclear Reactor (ITER) tokamak under construction in the South of France. This project isn’t even designed to produce net electric power. What it aims at is a sustained plasma burn from hot alpha particles, a “scientific milestone” far short of actual power output. Size matters, and even though it’s an interesting and relevant question why the huge ITER has its $12 billion R & D program, while SSP, intended for the same job of base load electricity production, has no money. The large size and capital investment to first power of both systems has to impact the business case. Ironically, it may be just because fusion is seen as a dream in the uncertain future, while SSP appears much more technologically mature that funding is so hard to get.

In the general soup of contemporary alternate energy discussions, diode laser beamers in geostationary orbit are a total game-changer for demonstrating space based solar power experimentally. We can build and test them now. Can we beam electricity into Iraq even as the insurgency blows up power lines? Can’t say now how much it might cost, but it’s certainly feasible in principle. My predilections are to demonstrate beaming power to some poor African village, winning the hearts and minds of our brothers and sisters in the developing world, as opposed to blasting them to bits, as some will certainly accuse developers of laser power beaming of. But the thing about any new technology is that you really can’t say at the outset where exactly it will go. What we can say with some assurance that no one has a clue how to build a small, cheap fusion reactor that would work. But we can almost certainly build an SSP with laser beaming now that would work; and build it small enough to fit into a single launch vehicle payload at a small fraction of the cost of ITER, or for that matter of FutureGen (DoE’s proposed coal-gasification to electricity and hydrogen pilot plant with CO2 sequestered), or one of DoE’s new design Gen IV fission reactors on the drawing boards. So I want to strongly agree with Jordin Kare’s comments on a the viability of an laser SSP demo expressed in his E-Mail below.

Indeed, we, my son Eric & I, have taken this idea further to the point of developing a 3-page report for DARPA: darpa-ssp-demo-exec-su_f2391.doc). But at least so far, we haven’t got very far. Perhaps it hasn’t been seen by the right people, or hasn’t become visible at the right historical moment. So I throw it into the ring once more as part of this discussion on the business case for SBSP. (We space power guys may not have any money, but we have the most acronyms: SPS, SSP and now SBSP).

92 Responses to “Technical Discussion On Power Beaming: Engineers Take Note!”

Alvaro Fernandezsaid

Has anybody thought of using “stratellites” (high-altitude airships) for this application? If you lofted the solar collector into the upper atmosphere (O(10^5) ft or so, I guess) you might be able to get most of the benefit of space beamed power, i.e. weather is not factor. But, you’ll be so much closer to the receiving station as compared to geosynchronous orbit that the scaling won’t kill you. Also, it would be easier to allay laser concerns since you (1) are lower so you don’t have as much of a field-of-sight issue, and (2) the lasers could be weaker anyway. I would envision one of these as powering a small city; a group could do a larger city.

The only two problems would be you’d have to expend some of your power in fighting atmosphering drag and drift, and of course you’d still have nighttime to contend with. Still, it would be useful and demonstrate the feasibility of beaming power.

I should note that one alternative path via 5 MW (in my comment on the preceding note) is to build a 5 GW-class solar power satellite but use lasers instead of microwave beams – even if the lasers are only an abysmal 0.1% efficient, you get 5 MW on the ground. The path to lower cost there is clear: raise the laser efficiency so you can lower the size of the orbital system. Diode lasers with power conversion efficiencies over 50% do already exist, so maybe we’re there!

Edawgsaid

live2scansaid

When I started communicating with this list I counted myself as a SPS proponent, but after spending time researching the subject, I must conclude that it is not the best solution. Let me explain.
I think that by listing both pro and cons I can show that a preponderance of evidence points elsewhere.
Pros for SPS: (1)It’s esentially a permanent and for all intents infinite power source, fusion power from a very large reactor.
(2)It requires less valuable land resources than ground based solar and is closer to 24 x 7 in output.
(3)A SPS can be sited at any equatorial point around the Earth.
(4)Because the power is so concentrated, conversion to chemical (hydrogen , ammonia or methanol) or other storage ( heat in a solar brine pond or phase change material) is facilitated.
(5)A network of satellites beaming power near or directly to the end user site would eliminate grid transmission losses and be difficult to disrupt, unlike pipelines or cables.
(6)Developing the technology and infrastructure to implement the system would facilite the commercialization of near-Earth space.

I’m sure there may be other benefits, I think I’ve covered the major ones.
Cons:(1)Cost, each satellite itself due to the need to have the lowest possible mass/output ratio and the difficulty of servicing problems that will arise (Hubble camera problems), must be made of the most reliable systems and lightest materials (read expensive)available.
(2)Since multiple launches will be needed to build any SPS worth having even if launch costs drop dramatically, the time for the deployment of even a partial network of satellites that can actually enable powering of many military bases or industries begins to stretch off into infinity (takes time to build boosters, transport and configure for launch, build and operate launch sites that have little other use,etc)
(3)Since beamed power is still not 24 x 7 some other method would need to be in place for known shade time and since system reliablity is a complete unknown, it’s a stretch to imagine that a commander or CEO would be willing to bet the ranch on a system with an unquantifiable reliablity factor.(How would you explain to your shareholders that your factory’s output will be zero until the repair mission that’s not able to be squeezed into the launch queue for 6 months)
These are showstoppers in my book and using lunar materials will someday happen, depending on them for a successful SPS deployment is not only putting the cart before the horse it would force committment to a model that is in my mind completely uneeded to acomplish the task at hand as I understand it.
“Produce reliable baseload electric power that can be brought online at a fraction of the cost of generating the same power from combustion and is more portable than ground based solar or wind and less subject to disruption from weather, enemy action or any other cause.”

I am utterly convinced that a constellation of Dark Sky Stations could produce equally concentrated beamed power that is more reliable than SPS and could be brought online in a vastly shorter time frame and for a small fraction of the cost of either a ground launched SPS or one built from extraterristrial resources.
The technology, airships, although not fully developed for this purpose, is mostly just reconfiguring existing technology to fit. In fact I’d bet that most of what Boeing had to create for their latest commercial jetliner (fly by wire and composite airframe construction)would be sufficient to produce a light enough platform for DSSPS (yes Martha another acronym) a Dark Sky Solar Power System.
Pros:(1) Low development cost-the technology to do this is virtually off the shelf, if you read Wired’s article (online) about JP Aerospace you’ll see that shelf might even be at Walmart.
(2) Short time line to implementation. Thin film PV cells are getting close to mass production even if SPS or DSSPS is never built and practical solar dynamic systems are being deployed today.
(3) Cost of deployment would be very low per unit. Using a JPA Acsender type airship to build/resupply/ maintain each station could be done from EXISTING airfields and be done virtually at will. The DSSPS is only a few tens of miles away vertically and could be sited DIRECTLY over the receiver not just in an equatorial orbit. That ability allows even polar regions to have beamed power.
(4)Since a DSSPS can be built to an arbitrarily large size multi-megawatt stations could be assembled from modular units to benefit from mass production economics. At the altitude of a DSSPS (see JPA’s site) there is litle or no wind so station keeping is probably simpler than with a SPS(no fuel needed,just electric props). I’d also bet that hydrogen could be used for bouyancy also, since even though it’s combustible there’s no O2 for combustion-more decrease in cost.
(5)The same platfrom design could be used for MANY other purposes-communications, enviromental monitoring, even tourism and many others, use your imagination. It would be easy to picture multiple DSS’s over every populated area since the cost of implementation once a standardized platform was available would be within the reach of much of industry and profitability would be in the near term and be vastly easier to quantify since the system components are familiar.
(6)Since the power beam must travel a much shorter distance than that from a SPS in GEO or even an LEO constellation, the receiver could be much smaller-increased portablity and again decreased cost.

I think that’s enough pros for anyone.
Cons:I can only think of two. The first is obvious, nightime power loss, even though the DSSPS is high up it still will have nearly the same shade time as a ground based system if losses for ground systems from clouds are ignored.
Two solutions come to mind. A system at the receiving site that converts a sufficient amount of the input to a stored form that can be used for times when the input is unavaiable is one.
The second implies a system that might eventually supplant the present power grid even for ground generated power. What if every DSSPS had on its underside a system of moveable mirrors ala TI’s Digital Light Processor and if a narrow power beam could be redirected horizontally
then surplus power from DSSPS’s or ground sites could be transmitted globally with a large enough constellation. Laser transmission losses would be less than the exixting grid losses and be reconfigurable in realtime.
The other con is a tougher nut to crack: the unwillingness of the powers that be to give up the idea of SPS for now and to focus their attention on a system that offers EVERTHING that SPS offers including bootstrapping space commerce at a price we can actually afford and in a time frame that is meaningful for people who are alive today.

On December 4, 2005 a team led by Southwest Research Institute (SwRI) successfully demonstrated powered flight of the HiSentinel stratospheric airship at an altitude of 74,000 feet (22.6 km). The development team of Aerostar International, the Air Force Research Laboratory (AFRL) and SwRI launched the airship from Roswell, New Mexico, for a five-hour technology demonstration flight. The 146-foot-long (44.5 m) airship carried a 60-pound (27 kg) equipment pod and propulsion system when it became only the second airship in history to achieve powered flight in the stratosphere.

How much weight can be put onto the stratosphere airships ?
Operating cost comparison ?

JP aerospace seems to have flaws for their overall goals. Getting up to 100,000 feet to 170,000 should be doable but how much they can hold is another question.

JP Aerospace’s design proposal was found to be technically flawed in an independent analysis by Robert Pickar. Specifically, the design assumes that electric propulsion, powered by solar cells, are sufficient to power the vehicle into orbit. In fact, the thrust generated by electric propulsion is insufficient to overcome atmospheric drag. Thus, the ATO craft would not accelerate beyond a low velocity.
Electric propulsion is inherently power-limited, that is, the thrust generated by an electric rocket engine is limited by the power of the electric power source supplying it. Given the intensity of sunlight on solar cells (the solar constant), there is a finite amount of electric power that can be generated. For ATO, this would amount to some 10 MWe. Electric rocket engines can produce about 25 newtons (6 lbf) per MWe of power. Thus, a maximum of 250 N (60 lbf) could be produced. Atmospheric drag on the ATO vehicle comes to about 11,000 newtons (2,500 lbf). The thrust is far lower than atmospheric drag, and the vehicle will not accelerate.
Additionally, the ATO vehicle would have power cut off during the night. JP Aerospace claimed that this would be handled with regenerative fuel cells. However, regenerative fuel cell systems have a specific mass of 600 W/kg. Replacing the solar cell power with fuel cell power would result in a large fuel cell. The system would be 100 times the vehicle mass itself.
These are all reasons why the ATO concepts appear to be unworkable from the physics standpoint in its present design. According to the skeptics’ claims, a different kind of propulsion, not limited by the available sunlight, must be used, and it is difficult to make any of the current technologies light enough for an airship design.

The record altitude for a balloon is 170,000 ft, winzen research balloon.

So they need to get better propulsion or launch something small and light that has less drag. close the 44 fold difference between propulsion and drag.

Mark Ellissaid

the problem with beaming energy back to earth is… what happens if something goes wrong with the satellite and it starts burning up the neighborhood. Keep in mind the dont have to be that far off angle-wise when your at GEO. 1 degree off and you may be lasing iceland and causing more global warming!

Mark Ellissaid

how is space based solar ever economically viable? it’s not even viable on the earth, without subsidies. until an idea can make economic sense it’s just [a waste of time].
improve solar on the rooftops (0 transmission loss) of the cities and towns that use the power… and use the power to lighten the load for power plants. perhaps when a space elevator exists space based solar wont be such a impractical idea. [I recommend] work on that!

JotaCesaid

I am new to these matters, but I have always had a doubt about beaming the energy to the Earth: I assume that the area around the beam would be a very dangerous one (lethal); that is, flight should be restricted around that area, and we would need a team collecting each day the corpses of the birds which entered the area. Is this correct?

Michael Handysaid

Umm, that passing reference to thin film radar got me thinking. Have thin film solar cells been discussed for use in orbit? They currently have very low efficiency (~8% if i recall) but they’re reasonably cheap, and are obviously able to bring weight down, leaving more for the bulky transmission array.

I’m not certain they don’t have major problems with radiation etc, but wikipeidia doesn’t mention them at all? So have they been proposed?

Des Emerysaid

Hey, Coyote — This is a bit off-subject but I don’t know how much you and your colleagues have been following international progress in solar power development. I just heard about the state of
Israel (one of the very few countries with absolutely no source of power internally) which has developed land-based solar power using a highly-reflective parabolic mirror to focus solar energy on an ordinary solar cell to obtain 1000 times the usual amount of electricity which can be pumped directly into use, without the necessity to convert the energy to boiling water to run a power plant.

At present they use coal-fired furnaces to produce the boiling water and feel the new application would clean up their air, and they have the desert conditions (‘sunny, sunny days’) that make the project feasible. Plus, the Israelis already are established in solar power in California.

They believe they now have the solar power facility and will concentrate on development of the target solar cells to improve receptivity. Whether or how this will affect your project remains to be seen, but I felt you should at least have the knowledge of the Israeli progress in land-based solar power. Perhaps their advances in mirror reflection – obviously a spacesaving feature – would reduce the weight-lifting of materials to LEO or GEO in your inquiries?

live2scansaid

This reply is mostly to Brian. I actually agree that an ion engine will not be able to accelerate an object with the air resistance of the ATO from the top bouyancy altitude to LEO. Another method is needed and may actually be available. Since beyond a certain altitude bouyancy is inefective at supporting the vehicle it could be dispensed with. If H2 were used in the ATO instead of He then a rather odd propulsion system might be used that would canibalize the gas for propulsion, esp. if the H2 was produced at the DSS from plain old H2O electrolyzed with solar electricity. H2O could be ferried up by Ascender flights, it could be regular cargo or just leftover ballast.
The H2 could be used to for ATO lift during construction and the O2 used by the crew and the leftover O2 liqufied.
The lox would then be available as oxidizer for the H2 in the balloon.
The kind of powerplant such a vehicle might use would depend in large part what you were going to launch and into what orbit,LEO or GEO. I’ve pointed out before in this blog that the ATO already has ALL the radial velocity needed for GEO,if sited near the equator, so that the vehicle just has to “get there from here”. Foreward velocity is not a significant problem since one is not trying to achieve LEO. What is important is to counterbalance gravity so that the ATO could travel directly to GEO. When first departing a DSS H2 bouyancy would lift it to whatever altitude was possible within the confines of its weight bouyancy limits. For the sake of arguement let’s use the JPA figure of 200K feet. At that point bouyancy becomes unable to raise the ATO any higher. If the H2 is used for fuel from there as long as the thrust produced is greater than the bouyancy lost then the ATO will continue to rise. Rise high enough and the gravitational attraction begins to decrease. Ye olde inverse square law. Maintain the same thrust and the vehicle speeds up, esp since by that time the atmosphere would be left behind. At some point the H2 would be exhausted and THEN an ion engine could take over and as long as it was able to maintain sufficient thrust so that the remaining drag of gravity didn’t overcome the initial forward velocity before GEO was reached you’d have a new SPS component.
What would that H2 powered engine be? Keep an open mind, please, how about a turbojet. What! Wait a minute they only work in the atmosphere. Well a turbojet usually commpresses air into a combustion chamber and injects a fuel to combine with the compressed O2 for thrust. How about a bit of a flip-flop,acompressor to compress the gaseous H2 and inject the oxidizer. The Isp is far less than an ion engine or arcjet, but thrust would be way higher. The thrust would peterout eventually as the lift cells emptied, but if you could maintain it long enough to escape from most of the gravity well. then you have just bootstrapped yourself to GEO. It’s a one way trip unlike the JPA plan, but I’ll bet it’ll work.

Coyotesaid

Alvaro: The major problems with high altitude airships is their instability (which is being worked on), their relatively small size in relation to the need to collect massive amounts of solar energy, and they are still subject to day/night and seasonal losses of power.

Arthur: Good points. A laser would save weight…but we need to take very definite steps to alleviate concerns about this being a weapon in any way shape or fashion. None of the energy beaming concepts I’ve seen to date could be weaponized due to the frequencies involved and the aperture sizes.

Edawg: No, these systems could not be used for asteroid/planetary defense. The energy is simply not there to divert massive objects or to dynamically aim the system even if it had that potential.

Des Emery – I’m in touch with David Faiman, the fellow in Israel who has been working on the concentrating solar power systems. It’s definitely a possibility; the main advantage is that it greatly reduces the requirement for solar panel materials, however it adds requirements for other systems, including active cooling and an accurate pointing system for the concentrator.

Space vehicles have flown with solar concentrator systems before though – Deep Space 1 in particular.

Coyotesaid

Live2Scan: You raise good points, but the day night problem with airships veiled by the atmosphere and limited in size makes them difficult too. Don’t worry. We are not saying space-based solar power is a “solution,” as you put it. It is merely another source of clean energy that gives 24/7/365 with the unique ability to beam that power anywhere it is needed. Expensive? Yup, but getting cheaper all the time. Do we want to see every available clean energy source developed? Yup. This is not a competition.

Mark Ellis and JotaCe: If you read the technical discussions you’ll see that the frequencies involved and the desaturation of the power broadcast prevent SBSP systems from being destructively intentionally or otherwise. But I understand your concern and am working to alleviate any concerns about these systems being used as weapons.

Michael Handy: We are looking at thin film arrays. To date they don’t have the efficiency or the robustness to last in the brutal space environment that we are looking for. But we expect they will improve and will be watching!

Coyotesaid

Miles Fagerlie: Glad you asked the question, and although we’ve had some that were related, you are the first to ask about solar updraft towers. No, we have not given that concept a look because that would mostly be a matter of ground-based solar power. Also, we are trying to avoid reflecting more sunlight into the atmosphere to avoid heating it up.

Why among the powerful and influential elites of the world, that includes but is not limited to the US President, are they not discussing SSP with urgency at the highest level of visibility? Where is the JFK saying that we WILL do this? Isn’t this an opportunity to rethink global economics and perhaps to achieve some semblance of utopia?

James Kiellandsaid

I’m no expert on the space elevator concept, but my understanding of it leads me to believe that one of the design parameters is an extremely light-weight cable design, most likely made from carbon nanotube. If I remember things corrrectly, one of the big technical hurdles is developing the capacity to create a ribbon of such material.

As to why the powerful and influential are not enthusiastically behind this concept, I will take a cynical view. The powerful are frequently eager to maintain the status quo as that is, in most cases, the source of their power. Oil company profits are at an all time high. If you’re heavily invested in the business of oil distribution these are very good times.

Virtually all of our federal transportation budget goes in to supporting ancient technology designed to burn fossil fuels. Our federal highway system amounts to a subsidy of both the trucking industries and the oil industries. That and our rail systems are so slow that increasing amounts of traffic of goods and people are moving into yet another fossil fuel guzzling sector: aviation. In the US, there is virtually zero money for R&D in other transportation methods.

A good start could be a revamped, electric powered rail network capable of moving materials, products, and people at high-speed across the country. This would serve to keep the country moving despite oil shocks. And would be a wonderful thing to plug in future space solar generated power.

Fundamentally, space based solar is just one part of developing clean energy usage. Right now, an unfortunate amount of our infrastructure is dedicated to burning fossil fuels and there’s tremendous inertia in our transportation sectors to keep that going. For space based solar to really be compelling, it will require more than jumping over a few minor technical hurdles such as launch cost and array construction. It will probably require a substantial re-ordering of vast parts of our economy.

And there’s a large number of “powerful and influential elites” who might take exception to that.

jwgormansaid

I am all for developing new solutions that provide alternatives to fossil fuel usage, and these satellite ideas sound really cool. But instead of killing a mosquito with a sledgehammer, maybe we should also approach the problem with the energy we’re already given. That is, if we “import” new energy from outside the stratosphere, couldn’t we be (eventually) setting the whole thing out of balance? maybe not more than we already have! but isn’t there plenty of energy falling through the atmosphere already? for the price of one test satellite, you could probably line up a lot of solarNodes on this network:

it’s also an experiment, but on a slightly smaller budget 😉 – and it doesn’t necessarily add huge amounts of energy to the mix, but counts on a combination of displacement of traditional energy sources, while increasing conservation. anyway this is great, will read on!

As to why the powerful and influential are not enthusiastically behind this concept, I will take a cynical view.

Quite the contrary…there are many of us who were once enthusiastically behind the space solar power concept, who having begun to work the real engineering issues behind it, realized that there were far better ways to accomplish the same ultimate goal.

Coyotesaid

TPM-Sarasota: 1) We are looking at space elevators and GEO cables as a possible disruptive technology to provide cheaper access to space and orbital transfer therein. Quite frankly, we are watching carbon nanofiber developments to see if industry can deliver a wire or ribbon 22,300 miles long that weighs a relatively few pounds, but can withstand the tremendous tension that will be required of it. We are also interested the interaction between such a system and the environment. 2) Gas masers vs diode lasers…good question. Does anyone reading this have a clue about the pros and cons of each??? 3)Regarding the “powerful and influential elites;” we are certainly trying to raise SSP to their attention, and our time is coming. Some are already on board, others are waiting to see how large we can grow our bandwagon. Right now we are trying to get our facts lined up and make a fair assessment of the work ahead of us. We need to do a lot of work so we can advise the “powerful and influential elites” effectively when the time comes…but that time IS coming soon. 4) Yes, SBSP WILL change global economics and we need to be aware and responsive to the concerns of other states and identitiy groups as the dynamics change. We want to make friends, not enemies. But will we achieve “some semblance of utopia?” I must defer to the political philosophers and theologists on that, but I feel confident that we will field our SBSP systems before that question is answered! Great comments. Thanks!

James Keilland: Nicely said. I agree. What makes the conduct of a study like this quite difficult is not the technical assessments of feasibility, or the business case, the environmental impact, or even the actual plan for how to get ‘er done. The difficulty comes when asking the “establishment” to change the way they think…to entertain shifting what might be their personal road to financial security…and to accept risks along the way that might be so very costly. In the end, it will boil down to two questions: “Is this this right thing to do?” and “Can I afford to do it (or not to do it)?”

Jwgorman: Your environmental concern is squarely on my mind and is at the fore of many discussions I’ve been having lately. We are working to model the effects of broadcasting power from space to our rectennas on the surface. The indications we have suggest there will be some increased heating, BUT, it will be exponentially less than the heat generated by petroleum-fired plants, coal-fired plants, nuclear plants, and petroleum fired automobile engines–and it well produce no carbon. You’ll be glad to know that we support the development of ALL clean energy sources and do NOT want SBSP to dominate the energy market. All states’ security is tied to having multiple clean energy sources and avoiding putting all of their eggs in any one basket. We want SBSP to be one of them, but it uniquely gives us a perpetual source of energy that can be broadcast anywhere it is needed.

Coyotesaid

Kirk Sorensen: You’re not cynical, you’re just lazy. Just kidding…just kidding. There is no doubt that the technical hurdles are huge and it will take a long time to overcome them. But what do you think the ultimate gaol is and how do you define “better?”

James Kiellandsaid

Thank you for your reply. I have my own skepticism of the near-term viability of space solar, as I’ve expressed elsewhere in this forum. Nevertheless, I take a rather dim view of attitudes that express “it can’t be done.”

My main point is that we are so heavily subsidizing fossil fuel, on so many levels, and that creates a situation whereby 1) people can’t point to alternative forms of energy and insist that they cost too much, and 2) large numbers of people are benefitting from the existing subsidies and will create enormous political resistance to change.

It could be reasonably argued that the current Iraq war, the vast number of bases in the middle east, virtually the entire US Navy have one primary purpose: delivering oil to the world economy. In our own country, there are vast additional subsidies to the DOT to administer the construction of highways which serve to subsidize the trucking and oil industries. Investments in other means of transportation or energy would be a threat to all of these existing interests.

I read with interest some of your writings on thorium. In particular, I strongly agree with your comment: “The generation and use of energy is central to the maintenance of organization. Life itself is a state of organization maintained by the continual use of sources of energy… Therefore, I embrace the idea that we need energy, and probably need much more of it than we currently have. ” Well said. Future economic breakthroughs are dependent upon what all previous economic breakthroughs were dependent upon: the discovery of new sources and applications of energy.

Whether that source is to be thorium, terrestrially based solar generation, space solar, or some other source is not something that I’d really care to get all excited about right now. Ultimately, I’m not sure that the technical hurdles are as challenging as the political and economic hurdles. And those political and economic hurdles are rather huge: making thorium affordable could be quite a challenge when vast subsidies are directed towards driving oil into the economy and the economy is built around consuming oil and not electricity.

making thorium affordable could be quite a challenge when vast subsidies are directed towards driving oil into the economy and the economy is built around consuming oil and not electricity.

I agree, and thank you for taking the time to read some of the things I have written.

I was involved with space solar power back when I was a grad student at Georgia Tech. We were doing work on super-lost space transportation systems to enable the deployment of space solar power satellites. The primary question to us was: how cheap does the “ride” have to be for SSP to make sense economically? So we had a big cost model where we made all kinds of incredibly optimistic assumptions about SSP technology: 50% efficient arrays with no radiation degradation, %0.25/kW*hr electricity costs in niche markets, giant carbon taxes on all our competition, no problems with power beaming or side-lobes, and free land for all the rectennas we’d ever want.

The real eye-opening moment came for me when my colleague, who was doing the cost modeling, typed in “zero” as the launch cost, and then proceeded to show me how the economic case STILL didn’t “close”. Now zero’s a pretty good number, bounding all kinds of cases like moon mining, asteroid mining, maglev launch from the ground, anything. It never gets better than zero. And SSP still couldn’t make an economic argument even at that number.

I’m not an economic modeler, and I’ve wondered many times over the years if there’s some missing piece that should have been included in the economic modeling that would have favored SSP. But I just can’t think of any–the inputs were already so SSP-favorable to begin with!

I was extremely dismayed by this result, because for many years prior I had put great faith into the SSP concept as the “way forward” both for the space program and for the world’s energy future. But after having participated in this effort, I could no longer honestly maintain that position.

Several years after this I learned about thorium and the liquid-fluoride reactor concept and began to have real hope again about our energy future. But unfortunately for me and other “space-cadets” (and I say that with love) a thorium-powered future doesn’t require a space program.

Edawgsaid

Coyotesaid

Kirk: Take heart in the fact that every business case model in the 1980s indicated that there was no future in cellular telephone technology. With every home and office having telephones, and every street corner having a pay phone, the predictions included that even if the cost of cell phones were $0.0 and calls were free, no one would bother to carry them. The point is that business cases are made by the customer, not the producer, and the producer can be way-wrong. Even if 100% of current energy needs were met by wind, ground-based solar, nuclear, and thorium, I still need space-based solar power to broadcast power to wherever I need it when I need it, for those times when it is unduly overcast in a region, the wind dies, or the protesters shut down the nuclear plant. Moreover, I need SBSP to broadcast power to regions suffering natural disasters, rapid energy consumption growth, etc.

I still need space-based solar power to broadcast power to wherever I need it when I need it, for those times when it is unduly overcast in a region, the wind dies, or the protesters shut down the nuclear plant. Moreover, I need SBSP to broadcast power to regions suffering natural disasters…

But that’s just it–you can’t do that with SSP. The physics of transmission (at least from GEO) essentially prevent you from setting up anything less than a 10-km rectenna to receive the power. That was the total shocker to me–to realize that a rectenna to receive a milliwatt or a gigawatt was the same size.

You’re not going to be able to drop into post-Katrina New Orleans and set up a rectenna and start pulling megawatts out of the sky, even if you had the SSP satellite. For a given transmission frequency, transmission distance, transmitter aperture, and desired efficiency, receiver aperture is fixed, independent of power transmission level.

No, SSP is not dispatchable power. It is an infrastructure-intense, fixed-base asset.

Coyotesaid

Maser and laser transmission from GEO lets me use small enough receivers to deploy them into areas in fairly short notice and to take advantage of a spot beam of energy from the satellite. The rectanna you are talking about is abour a factor larger than what is generally discussed. What frequency range are you talking about and what signal density are you using for your estimate?

Also, keep in mind that a single microwave transmitter can broadcast to a few diffent locations and with diferent intensities to each. There will be more rectennas on Earth than satellites on orbit.

Coyotesaid

The type of lasers and masers for energy transfer are coming along quite nicely. Refer, if you will, to the discussion of in the post that opened this discussion. The frequencies for these systems will likely be in the visible window extending perhaps as far into the near infrared as a micron of so in wavelength.

I’m not sure most people have a Death Star image of space solar power beaming, but if enough people are worried about it, a simple inspection of the lens, aperture, and related systems by members of the international community can quickly and decisively determine that whatever country launches such systems is not putting up anything that can be used as a weapon.

We are aware that many of the conspiracy theorists will never be satisfied no matter what. They may take comfort in the websites showing how to make a tin foil hats to protect themselves from such threats. 🙂

Your comments are excellent and most welcomed. Bringing SBSP on line is not going to be easy and it will take many years to get it more right than wrong.

James Kiellandsaid

I find the Death Star imagery to be so very curious. As far as “death from above”, it would seem that some kind of kinetic device could be much more lethal for a much lower cost. But beyond that, simple being able to beam power down is something extremely “weaponizable.” The theory is that directly beamed power reduces the logistics footprint from fuel. Very well. But the next biggest logistics footprint for forces is ammunition and the very heavy devices that fire that ammunition. Extensive electrical power opens up the possibility of some wonderful terrestrially based beam weapons.

It appears that we are moving ahead nicely with technology such as active denial, MTHEL, Airborne Laser, and so forth. It shouldn’t take much imagination on anyone’s part to imagine something like a Marine Expeditionary Unit being able to rapidly build a firebase, with a relatively light logistics footprint, which would be exceptionally difficult to assault. A rectenna, some beam weapons for dealing with aircraft, missiles, and mortars, and some to keep back people or destroy land vehicles. All without having to bring in shipping containers full of very heavy ammunition.

So, with this in mind I tend to snicker at those who are fearing the development of a beamed weapon in orbit. But I do realize that all new discoveries in technology and in particular the generation and distribution of energy have led to new weapons systems. Being able to precisely direct high levels of energy to any particular location on the Earth is such a huge change in the rules of the game. I think it might be a little naive to suggest that the Pentagon is only seeking a cheaper, greener way to keep the lights on.

I’m not sure most people have a Death Star image of space solar power beaming, but if enough people are worried about it, a simple inspection of the lens, aperture, and related systems by members of the international community can quickly and decisively determine that whatever country launches such systems is not putting up anything that can be used as a weapon.

Fine, I’m perfectly willing to ignore public perception and land costs. How much efficiency do you expect to get out of your laser and maser transmission techniques?

Coyotesaid

James Kielland: Um…I’m just working to determine the critical path to make space-based solar power feasible and how we can close the business case so industry can go about this. You identify some very transformational capabilities that might follow.

Kirk Sorensen: We’re not going to ignore public perception or land costs. We have to address each. The good news is that Japan, India, Australia, and Europe are also studying space-based solar power, so this is not just an American interest that will automatically garner international animosity. No one is accusing them of building Death Stars. We hope to work with them on this effort and to build broad international partnerships and to move this entire effort into the commercial sector at the earliest possible time. We are already discussing how to work with China on this as a way of cementing our relationship as partners instead of competitors. Regarding the land issue, I think you are referring to the real estate that will be used by the massive rectennas. This parallels the land used by ground-based solar farms that will only generate power during daytime and good weather–both being seasonally dependent. The SBSP rectanna farm will work continuously. But for those places where real estate is at a super premium, perhaps they will use a maser/laser receiver station and keep their footprint small. There is a lot of trade space here that needs analysis.

I repeat, what is the expected efficiency of the laser or maser transmission system you keep mentioning? I am withholding judgement on its merits until you can give me an efficiency now or in the near term.

Microwave-based transmitters and receivers are fairly efficient but have the fundamental physics problem of size. You have stated in another thread that you recognize that these systems are incompatible with the goal of a mobile, land-constrained forward base. Hence, I must conclude that you are counting on the laser/maser transmission technology. What’s the efficiency?

Coyotesaid

Marty Hoffert reports in the paper attached to the post that opened this thread:

“Diode lasers are commercially available (today) with 50% efficiencies at low power (Dickinson, 2002). Comparably efficient lasers with continuous power of hundreds of kW are under development for DARPA by our partner, General Atomics.”

Dan Lantzsaid

Land costs are not an issue, as you can live/farm under the rectennae.
More importantly, the Moon is so huge that diffraction problems are “focused” there, not by building large rectennae here. Major problem is when the Moon is not overhead. Either store or redirect energy with (before mentioned Michael #4 “The Goal…”) “space-based transmission from terrestrial power sources” satellites. These could be built for “quick fix” to high need military/humanitarian (now, if that’s not an oxymoron, show me one!) needs, and later be incorporated to LSP/geosyc system. Even geosync will need redirect to far North/South destinations.
Kirk #25,
Run the numbers again, with estimate that LSP is 50-100 times cheaper than SPS, and minimizes launch altogether. Also, Thorium makes steam, not electricity, right? Thorium on the Moon, to dump waste heat, perhaps?

This is rough; and assumes success in translating laboratory devices to larger scales with no drop in efficiency–an assumption that will be tough to accomplish with the likely temperatures that would be see at high powers…) BTW: the current technology readiness level for these devices (and high power and in space) is quite low; perhaps TRL 2-3…

Marty: any comments, corrections?

Best,

– John
____________________________

From: Marty Hoffert
Re: Maser/Laser Efficiency

Coyote:

I agree with John Mankins’ numbers for end-to-end laser efficiency near-term with two minor caveats: (1) These numbers neglect atmospheric absorption and scattering which might reduce beam transmission by, say, 90%. This is for clear skies, of course — clouds raising important, but certainly not insurmountable, issues. And (2) I’m not aware that diode lasers in the 200 kilowatt class, which we’d like to employ in a space power-beaming experiment, exist yet as operational hardware (John has noted this). Though researchers are working hard on it. I have the impression DARPA is developing these for various military applications. To my unclassified knowledge they’re not “on the shelf” but could be with the right push. If not we can do our proposed space-to-Earth laser beaming experiment at lower power and learn a lot while significantly advancing the technology of SSP…

Dan Lantzsaid

Kirk:
“Free launch bounds the case of asteroid or lunar materials, since they’ll never be cheaper than earth stuff”
You’ve obviously missed the whole point! Earth cannot supply enuf to bioize space, at any cost, let alone allowing us to keep on going as we are. The environmental cost of Earth based energy is killing us already. I would say that exoterrestrial materials will be cheaper than Earth stuff for the rest of time, starting soon! Glad you agree that waste heat is a problem with any Earth based heat engine, even if only by avoiding the issue!

Yes, the data helps, but it does not help the SSP argument. What it says is that the efficiency hit from going to laser transmission and tailored PV receivers is SEVERE. 36% efficiency for a system that John Mankins describes as “tough to accomplish”. Having been on the receiving end of some of Mr. Mankins’ ideas in the past, when he calls something “tough to accomplish” I would call it practically impossible.

So you’re back to microwave transmission at 80% efficiency and huge transmitters and rectennas. Not a system for a mobile operation in a remote site. An expensive, fixed-base asset.

Coyotesaid

I am not worried one iota about the business case for laser transmission of space-based solar power transmission. I am currently paying $300 to $800 per gallon (Chris Dipetto’s calculation) for fuel delivered to Iraqi generators…that burn at 14% efficiency and are taken out almost daily by insurgent rocket attacks. The majority of US casualties have occurred during convoys of this energy through the cities of Iraq. 70% of my entire logistics train is dedicated to moving petroleum. If you do the math, you’ll see that even at multiple dollars per kilowatt hour I am saving money…and lives. The later being the point.

Having grown much older under enemy fire, I ask you again to calculate the business case…with regard for those guys and gals in the blackness of Darfur tonight…and in Peru whose dead we can’t even count once the sun goes down.

There is a “priceless” quality of some energy during some times. That’s one of the commodities that laser broadcast of space-based solar power delivers.

A.C.said

As a thought for different SPS energy trasmission approaches and to generate new ideas…
“The diffraction limit on electromagnetic waves is a fundamental law of physics built into the structure of this universe”. Not completly true, the fact is that in the near field environment evanescent electromagnetic radiation is not diffraction limited. Perhaps we are looking at the wrong end of the spectrum with 2.4 Ghz, “I’m in a SPS side lobe zone-Oops, Kiss my WiFi home network goodbye ” or the near IR visible spectrum range, with possible biological plant/vegetation effects.

EVERETT L WILLIAMSsaid

The possible and useful should be approached before the extremely unlikely and difficult. It is unlikely that a terrestrially based space elevator will be built any time soon for many, many reasons, both technical and political. On the other hand, we have already in hand most of what it will take to build a lunar elevator to the Earth-Moon L1. This will drastically reduce the cost of obtaining materials for GEO construction from the Moon. Frankly, I don’t believe that Kirk’s buddy in Georgia did his math correctly on the costs of orbital power. Certainly, all such calculations suffer from the improper attributions of the actual costs of the use of fossil fuels. We contribute to those costs at so many entrenched levels that it is difficult and sometimes impossible to ferret out actual costs. If we find an adequate source of water on the Moon, the calculations will again be completely altered. Assuming that almost all materials and consumables for the orbital power stations will come from the Moon, using a combination of a space tractor and an elevator, drastically reduces the costs of building and maintaining such a system. Once we are free of gravity well considerations, it is not only SBSP that comes into focus.

jwgorman,

The satellite solution will reduce the amount of heat and greenhouse gas released into the atmosphere, not increase it, because a process that turns all the inefficiency into waste heat in the atmosphere will be replaced by a process approximately 80% efficient that releases very little heat into the atmosphere. Just getting rid of most of the mining for coal, especially strip mining, will more than compensate for any possible environmental damage caused by SBSP. Proper spacing of receiving stations will also reduce transmission losses for electricity. If lasers are used to send down spot power, most of the inefficiency and loss in that system will occur in space rather than on the planet, again limiting impact. And, the solar network you refer to is nothing but bookkeeping. It adds not one watt to our resources, while consuming watts to track. The only way solar is going to actually provide watts 24/7/365 is to move it into GEO. Then we won’t have to play stupid accounting tricks to convince ourselves that solar is really beneficial.

EVERETT L WILLIAMSsaid

Reflecting light back into the atmosphere will not heat, but cool the earth. The major mechanism of solar heating is absorption and re-radiation as infra-red. Reflection of light, as in glaciers and ice sheets cools the Earth. That is why the loss of such produces a tightening feedback spiral.

John H Williamssaid

Space beaming energy from the Sun to the surface of the earth is the best way to do the job right. Store the energy in Condensers, and transmit the energy into needed resources directly.
That is my two cents worth,
John

Alienthesaid

I see much of the discussions here relate to microwave or laser beaming to the ground. Would I be leaving the box too far behind in my thinking if I propose not to convert the energy before beaming to Earth?

Why not sell the energy as optical, split by wavelength:
– IR/red : heating, much needed in disaster relief – think Bam and Pakistan in recent years after earthquakes
– yellow : illumination at night of, say, big cities, save energy on streetlights and vehicle headlights. On the night side you will have eternal day. Often I see the allies own the day and the insurgents own the night.
– green : experiments are underway with high speed communications with submerged submarines using green light that penetrates seawater to some extent. They need lots of power and here is a way to provide enormous powers.
– blue : scattering light is useful for creating a blue sky without sunlight, just like the sky just before sunrise.
– UV : directed to upper atmosphere to regenerate ozone.

Filtered light at energies just above the band gap in solar panels can provide extra light for ground based solar panels without the excessive heating problems you get with concentrators alone.

How to do it? Use the Sol-Earth Lagrange point L2, in the shape of an annulus of a mirror, 6000 km inner radius to stay just outside Earth’s shadow. Make a hub with thin wires to the circumference, make it rotate very slowly to keep it well tensioned. Use wires to control mirrors in sections.

This is not my idea; I saw this years and years ago but I cannot find anything on the net just now. Someone with a better memory and at NASA will probably find this.

Just some numbers: 1m wide strip, 40000 km long, 1 um thick is 40 cubic meters. Using Al the weight is not astronomical in terms of current technology. No big science needed, just big engineering.

One snag: L2 is a point and as such it is a unique piece of space real estate with a value. Others might want a piece of it or compensation for what most likely will be US corporations running the show. I can see ugly politics here.

Slight upside: solar pressure can be used to move it slightly sunwards from L2, freeing it for others.

The project works by storing sunlight-based energy in plate made from a sintered powder of metals like chromium and neodymium. When weak laser light is shined onto the plate, the stored energy is transferred to the laser where its strength is amplified by a factor of four. In one test, a 0.5-watt laser was amplified to 180-watts by the plates. Scientists have thus far been able to garner 40-percent of the solar energy produced, and they hope to have a system ready for satellite mounting by the not-too-distant year 2030.

The Japan Aerospace Exploration Agency (JAXA) and Osaka University’s Institute of Laser Engineering unveiled a new method for converting sunlight into laser beams—a superconducting metallic plate that amplifies light 30 percent more efficiently than previously possible, then shoots back the intensified energy to power stations on Earth.

shaunosaid

Ok what about 20km2 or 50km2 solar arrays in the Australian desert regions while not as efficient as a space based solar array surely it would be multiple times cheaper. Only problem it wouldn’t be able to produce power overnight unless we could store the energy some how for sustained release. If we could combine it with nuclear power during the night and solar during the day it would be perfect.

Ive always been disappointed that Australia hasn’t shown leadership and vision in this field as we have essentially unlimited amounts of land bathed in hot sunshine. And this is coming from a career oil and gas man.

Ken Beyersaid

Shauno. There IS a large scale storage method that was origionally developed in Australia but is now based in BC, Canada. It is called the vanadium redox battery. This technology is already being deployed in various locations in the world at small scale requirements . BUt this is progressing nicely, to the wind farm stage. VRB Power of Richmond, BC has partnered with many entities world wide to bring this into production/usability staus.
Check it out. http://www.vrbpower.com
Cheers!
Ken Beyer
Eagle Bay, BC

jwgormansaid

my point was that when you look at the way the earth works, there’s a lot of energy beamed from the sun to “power” living things. there’s already a lot of energy actually that makes its way through the atmosphere. so far with our research we have figured out how to get 15% of it out of the sunlight. I as a consumer can get 15% out of the sunlight, without a satellite program. (ok, closer to 40% in the labs) Well – there’s another 60-85% left to squeeze out. There’s algae that uses 95% of it, so it’s possible. the idea that you take solar energy from outside the earth to power stuff on earth WILL work – the same way digging up oil and burning it WILL work – but it’s not getting us closer to the way the earth’s total energy balances, which we shouldn’t mess with, if we can help it. I’m not against space-based solar compared to fossil fuels, but probably we need to tap every source of power we can, without depending on any of them too much. but what about conservation and efficiency? that’s effectively the same as an energy source – well, ok, if you take an interest in accounting.

Also you say that it takes more power to do the bookkeeping than it would generate – what kind of computer are you thinking of? an older dual P4 with noisy blower fans and air-grills on it running Windows 2000?? take a look at these:

Neil Coxsaid

Please forgive me for edit, cut and paste of the original post: A million people have thought of using “stratellites” (high-altitude airships) for this application. If you lofted the solar collector into the upper atmosphere 100,000 feet or so, you can get most of the benefit of space beamed power, i.e. weather is a minor factor. But, you’ll be so much closer to the receiving station as compared to geosynchronous orbit that the scaling won’t kill you. Also, it would be easier to minimise microwave and laser concerns since you (1) are lower so you don’t have as much of a field-of-sight issue, and (2) the lasers could be weaker anyway. I would envision one of these as powering a small city; a group could do a larger city.

Problems would be you’d have to expend most of your power in fighting atmospheric drag and drift, and of course you’d still have nighttime to contend with. Still, it would be useful and demonstrate the feasibility of beaming power.
Me: Yes, let’s start buiding grey sky station. JP Aerospace exaggerated about how high we can get dark sky station without CNT with excellent specs. If we think international, we don’t need to fight drift. The power station will drift around Earth several turns and can be recovered near the Arctic Circle. Three grey sky power stations can be kept about one kilometer apart. One with the concentrating mirror suggested by the Isralli. The trird station is connected by a flexable power line to the transmitting facility which must be pointed precicely at the receiving station on Earth’s surface. How close are we to mass production of the solar panels which can tolerate 100 or 1000 times sunlight energy? Neil

Neil Coxsaid

Hi alienthe: I had not heard much of that before. Surely L2 is more than 6000 kilometers from Earth, and moves enough that it is a volume that can be shared by many users. The problem is the sun is not a point source, but has a diameter of about 1,300,000 kilometers. If we could position a one square collumator near the mirror, to get the sun beams parallel to each other, we can perhaps produce narrow beams of red, orange, yellow, green, blue and near ulta violet light for specific uses on and near Earth.
The strip you mentioned has a mass of about 100 tons, so we can get it to LEO = low Earth orbit with near term technology, but I think you have a much farther destination in mind. More later. Neil

Neil Coxsaid

Please forgive my copy, paste and edit: What if every DSSPS = dark sky solar power satellite had on its underside a system of moveable mirrors ala TI’s Digital Light Processor and if a narrow power beam could be redirected horizontally
then surplus power from DSSPS’s or ground sites could be transmitted globally with a large enough constellation. Laser transmission losses would be less than the existing grid losses and be reconfigurable in realtime. Me: I think this is workable with a few thousand grey sky stations at 100,000 feet, we can cover most of the USA with an airbourn electric grid, assuming the laser diodes are better than 50% efficiency. In what year can we expect to manufacturer the trillionth laser diode of this type? Can we expect failure of the balloon when a laser beam is aimed wrongly?
More of you: The other con is a tougher nut to crack: the unwillingness of the powers that be to give up the idea of SPS for now and to focus their attention on a system that offers much that SPS offers including bootstrapping space commerce
Me: I’m not conviced even 200,000 feet altitude does much to bootstrap space.
More of you: at a price we can actually afford and in a time frame that is meaningful for people who are alive today.

Neil Coxsaid

With large enough optics, a million laser diodes can be deadly to humans from a balloon platform 36 kilometers away. I don’t think this is possible from 36,000 kilometers away = Geo stationry altitude. The closer deadly condition is better adapted to propulsion of an armored troop carrier, and small encampents, where a safe 1000 square meter energy receiver would be impractical = one megawatt at an average of one kilowatt per square meter = 0.1 watts per square centimeter, which is rarely harmful. The latter is the max allowable leakage from a microwave oven. Lasers require extreme caution when they exceed 0.1 watts per square centimeter = one miliwatt per square millimeter, due to possible eye damage. Laser pointers are dangerous at very close range. Neil

Neil Coxsaid

We need to test rectenna theory between mountain peaks to determine the minimum power density of the incoming beam. Silicon rectifier diodes produce negligible output at 1/2 volt (and less) ac input, and may be useless at 2.55 gigahertz. Does anyone manufacture a power diode for one millimeter waves = almost infrared? Can they be mass produced? It will be a considerable disadvantage, if we need a million diodes for each kilowatt of dc out. Are we going to use a 300,000 dipoles per square meter if we are receiving one millimeter waves? I suspect we are not sure, but these and other answers can be obtained for about one million dollars worth of mountain top testing, if we can use existing, but highly classified equipment as the source of the one millimeter waves.
The only rectenna test, I’ve heard about, lost 70+ % of the transmitted beam. Some think we can get 90% efficiency in the rectenna, but has 30% efficiency been demonstrated?
I suppose we can graze beef cattle in a 0.1 watt per square centimeter beam 24/7 in cool weather, but has this been tested? That would be a 0.2 watt beam before it passed though a rectenna which removed 1/2 of the energy.
I think the laser energy receiver has already been tested to a megawatt or more, but farther scale up may be unproven. Neil

Neil Coxsaid

Scale up looks good on paper, well into the megawatt range, but there are many possible problems in the gigawatt range. A thin film array that covers several square kilometers will have unexceptable resistance IR losses, unless the output voltage is perhaps ten million volts times 100 amps = one gigawatt. How do you switch off ten million volts? Vaporizing 100 meters of the power line with high explosives might work, but makes turning the power back on difficult. Even at 100 amps the main bus bars may have more mass than the thin film. If we have an hour to turn off the power, we can rotate the several square kilometer thin film array about 100 degrees, so that negligible light is falling on the photovoltaic cells. Faster rotation will require robust constuction and many rocket motors or ion engines to accelerate the turning rate.
If each klyitron needs 100,000 volts, we can connect 100 of them in series across the ten million volt bus, or 2,000,000 laser diodes that need 5 volts each. In either case shorted units may be a minor problem, but open units will have perhaps a one megawatt arc, which will damage other nearby units and structure. How do we make repairs to either the thin film photovoltaic array or the klyitrons or the laser diodes without shutting down the entire system?
The Israllii mirrors may simplify the shut down proceedure, as they only need to turn five or ten degrees for the beam of sun light to miss the photo voltaic array.
I was once one of about 100 persons who opreated a 0.7 gigawatt oil fired electric power plant. Something needed repairs every day, so I find it difficult to imagine remote operation of a steam turbine system from 36,000 kilometers away. Neil

Alienthesaid

Yes, this Sol-Earth L2 point is 1,500,000 km away so number do get big. On the other hand you can use the structure for long optical paths to get good collimations. One way is to reflect and concentrate by mirrors on the periphery to wavelength splitters on the hub and then large aperture light guns on the periphery for a total path of 12,000 km.

In fact having simple tech on the periphery and high tech on the hub would simplify installation and maintenance.

Scales are mindnumbingly huge but it is all low technology. Station keeping using solar pressure is the only obvious problem I can see.

I am still trying to remember where I read about this but I just cannot remember. Hopefully someone else will remember. It might have been in a project relating to terraforming Mars type planets.

Neil Coxsaid

We don’t know the efficiency of a large SBPS = SPS because no one has built one nor even the components of the system nearly that large. Also there are likely several different approaches which are workable. We can make an educated guess either high or low depending on weather we want to show it will be money well spent or folly. I will try to be neutral. We put ten square kilometers of thin film photovoltaic cells at an altitude of 36,000 kilometers. The cost of the film is trivial compared to the cost of delvery to 36,000 kilometers altitude, but the space elevator (if it succeeds) should deliver to GEO at perhaps $500,000 per ton in 2007 dollars. The giant panel is kept facing the Sun 24/7. We can likely ignore the few hours per year when the Earth gets between the panel and the Sun, but that will be inconvenient for the homes with no electricity.
Let’s assume the as built efficiency is 16% including the million? kilometers of conductor that interconnect the billion plus cells in series parallel to produce ten million volts at 180 amps = 1.8 gigawatts. The panel has 9 square kilometers of active area = 9 million square meters at 200 watts output per square meter = 1.8 gigawatts = about 16% effeciency. We will include the modest power loss in the ten kilometer flexable power cord that connects the photovoltaic panel to the laser diode panel which must point at the the receiving site on Earth. Let’s assume one billion laser diodes with an output of 0.9 gigawatts = 50% efficiency including the small wiring losses.
0.7 gigawatts = 700 megawatts illuminates the receiving site. 100 megawats is reflected back into the atmosphere by the site. 50 megawatts heats the ground and cows under the receiving site. 50 megawatts heats the photovoltaic panels which produce 500 megawatts of low voltage dc power. This is a large receiving site, so there is significant wiring loss conecting perhaps 3000 photo cells in series parallel to each inverter. The outputs of the inverters are connected in 3 series strings to produce 3 phase ac for the power grid. At 500 volts RMS output each we need 1000 inverters in series if the power line voltage is 1/2 million volts. By doing it this way we avoided using any transformers. Transformers with hundreds of primaries would likely be less than 50% efficient with a step up ratio of 1000. Inverters are still getting better, so we might put 400 megawatts on the grid. The sun light falling on the thin film was about 1000 watts per square meter = ten billion watts falling usefully on the ten square kilometer array = 4% efficiency. 3.6% if we figure the full 1275 watts of sunlight falling on ten instead of 9 square kilometers. The efficiency is much better if we start at the dc input to the billion laser diodes = 1800 megawatts = 22 % efficiency. The efficiency is likely a bit less using the Isralii concentrating mirrors, and the cost of the first ten system may be higher due to the added complication. It appears the Israllii concentrators may be necessary for systems that deliver more than 400 megawatts to the grid, if we want an emergency shut down time under 5 minutes.
If each diode requires state of the art optics, the optics may be 1/2 of the total cost.
Each inverter operate at 1250 watts output, so we can scale up some before we are looking at series parallel inverters.
Please note: About 300 megawatts is scatterd about the solar system. The laser diodes can be modulated with wide band data which may be more valuable than the 400 megawatts put on the grid. A modest receiving system can receive this broad band data at about 1/2 of all Earth locations plus 1/2 of solar system locations, including sometimes far beyond Neptune. The microwave system also provides this valuable data broadcast option at little extra cost, unless we use magnetrons. Neil

Alienthesaid

But that’s just it–you can’t do that with SSP. The physics of transmission (at least from GEO) essentially prevent you from setting up anything less than a 10-km rectenna to receive the power. That was the total shocker to me–to realize that a rectenna to receive a milliwatt or a gigawatt was the same size.

You’re not going to be able to drop into post-Katrina New Orleans and set up a rectenna and start pulling megawatts out of the sky, even if you had the SSP satellite. For a given transmission frequency, transmission distance, transmitter aperture, and desired efficiency, receiver aperture is fixed, independent of power transmission level.

No, SSP is not dispatchable power. It is an infrastructure-intense, fixed-base asset.

Lets just run the numbers again with optical wavelengths rather than microwave. Wavelengths:
uWave: 1E-1m (corresponds to 3 GHz)
light: 1E-6m (actually visible light is a little less than that but I just want to keep it in the order-of-magnitude style)

Ratio then is 1E+5 and since diffraction scales inversely with wavelength it means your 10 km spread just dropped down to 1m, so for all practical purposes the footprint on the ground is just the projection of the aperture of the light gun in orbit. Now you only need a 10 x 10 array 10 m aperture dishes which is reasonably mobile and no longer infrastructure-intense. If you only capture 10 percent of the transmitted power it is still a lot and quite possible worth it for military operations.

Neil Coxsaid

Post 61: Alienthe seems to be saying that a 100 meter square = 10,000 square meters will cover most of a minimum size beam of 1000 nanometer near infra red light. At 10 killowatt per square meter, we can put 100,000 kilowatts onto that receiver area, assuiming we can crowd one billion laser diodes at 1/10 th watt each into 10,000 square meters at the transmit platform 36,000 kilometers away. I believe that puts the diode centers about 1/3 centimeters apart, so that may be possible. More power per diode would reduce the crowding. We may have to choose less than 10 kilowatts per square meter, which would improve the safety or halve the wave length which I believe is yellow light = 500 nanometers. 400 nanometers is blue or violet or indigo. Is there any chance the 50% efficiency laser diodes will be possible in near ultraviolet = about 380 nanometers? Every little bit helps if we want a beam density of 10 kilowatts per square meter or more in a bit less than 10,000 square meters?

Moon-Earth L2 is 42 times farther away, so I presume the minimum spot diameter is about 4200 meters at 1000 nanometer near infrared light, unless Alienthe is saying we can collimate part way to Earth. I’m confused by post 59. Can someone clarify?

Neilsaid

Coyote:
If the existence of oil has brought us to war; such that we have a situation where people will fight for the privilege to pay $20 a gallon for a fuel that burns with 14% efficiency, has all the drawbacks you’re talking about – and those who cannot fight for that privilege (Darfur) simply sit in the dark and starve, what makes you think SBP will change human nature?

We (humanity) may solve the engineering problems, and succeed at this project. But mark my words: we’ll still get a bottlenecked, (by legislative fiat) competition-free energy market, with government-enforced artificial scarcity, people forced to fight-or-starve for access to energy, and all the unhappy ugliness that goes with it.

In 1976, when I was 9, I saw Dr. Gerard O’Neill give a presentation on SBP (and lunar-based mass drivers) – since then, we’ve built and launched, and retired the Space Shuttle. The arguments for and against SBP sound very much the same today as they did then. I’m not taking a defeatist-tact here, I just think we’re overlooking some of the fundamental difficulties that make us even WANT SBP in the first place – and those problems are not solved by SBP. Even massive deployment of SBP would only be a band-aid.

Neil Coxsaid

I did not type #64: The existence of oil has brought us to war. We (humanity) may solve the engineering problems, and succeed at this project. In 1976, when I was 44, Dr. Gerard O’Neill give a presentation on SBP (and lunar-based mass drivers) – since then, we’ve built and launched, the Space Shuttle. The arguments for and against SBP are very much the same today as then. Neil

Alienthesaid

Note that aperture is for the planar wave going out, so if you use lasers you must have them all cross coherent with each other, otherwise the effective aperture is that of each laser in which case diffraction spreads the beam all over the place. Microwaves can use a common clock signal to maintain coherence, lasers require far more sophisticated setup, possibly beam feedback

A plain reflection from the sun will work since the sun-earth distance is long.

atmospheric scattering While blue light spreads less by difraction than red the atmosphere scatters blue more than red. Blue is most prone in our atmosphere so green is perhaps most effective. A light beam would nevertheless look impressive from any distance, and blue light can have its uses as scattered light too.

atmospheric refractionWhat makes light from stars twinkle can make an optical beam wave too. Not sure how much though.

BTW UV-lasers would have low efficiency and be very recent technology and the beam would be absorbed by atmospheric ozone. Why would you use it?

Neil Coxsaid

Hi Peter Wilson #63 Large SBSP will need rockets or other propulion occasionally to stay in their GEO slot. Even 30 square miles of solar panels only produces a few pounds of thrust, so the station keeping energy needed is tiny. For non-geosychronous orbits years of drift will hardly matter at all. The 4 echo balloons are in essentially the same orbit after 50 years. Altitude about 400 miles.
Solar sails are over rated = not an enormous velocity increase, unless the solar sail has tiny mass, and almost no payload, even with 30 square miles of sail. Neil

Neil Coxsaid

I’m sketical about the wheel with 6000 kilometers inside radius for L2, but if we build it in LEO = low Earth orbit, of extremely light construction, such as 100 tons total; solar wind should push it a few hundred kilometers toward the shaded side of Earth. It can then reflect sunlight into the sunset and twilight band of Earth, allowing collection by photovoltaic panels, green plants and concentrating mirrors for an hour or two after sunset. This is important, as this is the peak electric demand period in most locations. The reflected light would appear to be coming from the East or overhead as the sun set in the West. Neil

Alienthesaid

I’m sketical about the wheel with 6000 kilometers inside radius for L2

Just curious, why are you skeptical? We already build transoceanic cables that are longer and have been doing so routinely for decades. The big advantage of such a wheel is that it also is scalable: when you need more power you do so by adding more panels to the circumference by sliding from the hub to the periphery where most likely a robot would receive it and place it into position.

if we build it in LEO = low Earth orbit, of extremely light construction, such as 100 tons total; solar wind should push it a few hundred kilometers toward the shaded side of Earth.

Considering LEO spans 200 – 2000 km I would say a displacement of only 100 km would cause de-orbiting, the gradient is rather steep this close to Earth and solar pressure is not that big. I owuld also like to see a calculation of the drag of the residual atmosphere for a structure as large as this.

It can then reflect sunlight into the sunset and twilight band of Earth, allowing collection by photovoltaic panels, green plants and concentrating mirrors for an hour or two after sunset. This is important, as this is the peak electric demand period in most locations. The reflected light would appear to be coming from the East or overhead as the sun set in the West.

I believe the purpose is good. Twilight extension can also be had using mirrors in the stable Sun-Earth L4 and L5.

Neil Coxsaid

Hi Alienthe: I did not mean, it can’t be built at l2, but it would be much more costly, than in LEO = low earth orbit.
More important most 99% of reflected energy would miss Earth. This is because the sun is not a point source, but has a diameter almost 1/2 of the beam length. Possibly the beam could be columated, but my guess is not practical.
Pushed a few hundred kilometer toward the shaded side of Earth, would, I think require slowing the spin a bit, as it’s RMS = root mean square mass would be a bit farther from Earth than in LEO orbit. You are likely correct that the solar wind is only strong enough to displace the orbit perhaps 100 kilometers, which won’t allow sending significant light deep into the twilight zone. Neil

Neil Coxsaid

Me: I copied, pasted and edited from http://www.space.com to illustrate the problems with large solar sites on Earth’s surface, some of which will apply when we build very large scale in LEO or on balloon supported platforms:
e says: The five megawatt facility being developed in the City of Mendota, California….
h says: That’s a pipsqueak compared to a 177 megawatt solar-thermal facility soon to be built not far from there:

California Valley might soon get a few shiny new neighbors, from a solar power plant proposed for rural San Luis Obispo County.

P.G.&E. and Ausra energy have announced plans for a 177 megawatt power plant using flat mirrors to make the plant cheaper and more efficient.

The project would be located between Paso Robles and Bakersfield near the Carrizo Plain.

The plant is being proposed for a sparsley populated area on one square mile of land that Ausra already owns near the Carrizo Plain National Monument.

Power companies must provide 20 percent of their output from renewable “clean” resources by 2010.

The plan will take a year to review, with possible construction starting by 2009.

t says: Nearly every form of power is reliant on subsidies, be it coal, oil, or nuclear. In 2004, $150 billion was made available to subsidize fossil fuels, with $53 billion dedicated to coal alone.

Me: A square mile is about 2,600,000 square meters. 177,000,000 watts divided by 2,600,000 = 68 watts per square meter, so they are getting high utilization of the one square mile, unless most of the flat mirrors will be on adjoining property. Since a flat mirror on a tower is no uglier than a cell phone tower, the neighbors may be cooperative. The mirrors can be turned to provide extra light in yards and gardens when the angles (or light level) are wrong for the photovoltaic panels. It is challenging to get much more than 68 watts per square meter except at 1 pm on June 21, as the mirrors will shade each other and some of the photocells early morning and late afternoon. Also walkways must be provided to clean a large photovoltaic array and do other mantainance. The panels would be much more costly to allow walking on them, plus their working surface is likely dangerously slippery. A beam more than a mile long scatters some of the light beyond the photovoltaic panels, so it will be difficult to scale up to more than about 177 megawatts without some diminishing returns.
I would like to see “as built” results compared to promised results for some completed systems. Does anyone know where such data is available that is truthful? Neil

AKsaid

Hello all, my previous post seems to have been lost, so I’ll repost and rely on the moderators to delete it if it’s a dup…

I’ve been ignoring the laser options as probably not feasible, but I had time to do a little research, and I may have something workable.

First some useful facts. There is a window from about 0.25-0.3 microns to perhaps 0.8 microns (near UV, visible light), as well as several somewhat “dirtier” windows in the near IR. Here is a graph of the atmosphere’s transmittance between 0.4 and 2.5 microns. The direct beam transmissivity is a little higher than the figures in the graph I linked, so I suspect this one is integrated over a hemisphere. My source is page 118 of Marshak and Davis. Beyond the range of the linked graph, it shows a dirtier window around 3.5 microns, and an even dirtier one at around 10. (This is the thermal IR region involved in the greenhouse effect.)

After that, the atmosphere is essentially opaque, until you get to a very dirty window peaking at about 3.5 mm, a somewhat better one at about 10 mm, and it’s transparent from about 18 mm up. Those are the wavelengths available for power transmission.

An advantage of using lasers feeding PhotoVoltaic cells is that such cells have a “natural” voltage they operate at (the band gap), and maximum efficiency will be obtained at a color with a photon energy just a bit above that (in electron volts). I presume this is how you expect to get the 50% efficiency for the ground station (since lasers are monochromatic). To convert from wavelength to photon energy, go here.

Now, for efficiency at the power station. I’ll point out that the correct efficiency is not the ratio of power output to solar power received, but a ratio of power output to station mass. This permits a technology that was (1/2) mentioned above: solar pumped superradiant gas lasers. The best-looking type I could find is based on copper vapour, but there may be other metal vapours that would work better.

To make a gas like copper vapour superradiant, a very long path is required (AFAIK). The beam will have to primed with the output of a standard gas laser with a proper cavity, which is then focused by a 15 meter mirror down a tube of plasma 15-20 meters in diameter and several hundred meters long, which is at the focus of a parabolic cylindrical mirror focusing sunlight to pump it. (The priming laser will have to use the same gas as the main amplifier, I’m assuming copper vapour here.)

Now, let’s assume an energy efficiency for the laser of 1%. A square kilometer of mirror can capture, say, 10^9 watts, which means we’re left with 10 megawatts in the beam, say 4 megawatts delivered at the wire on the ground. A square kilometer of 10 micron aluminized film might mass 25 tons, let’s assume 75 tons for the supporting structure. For containing the metal vapour (plasma), assuming a magnetic field generated by a coil of aluminum 1 square cm. in cross section, 15 meters in circumference, wrapping once per meter, that adds up to ~15 tons. You’d also need power for the current and the priming laser, presumably from PV cells, as well as the priming laser itself, metal vapour handling structure, etc. If we assume a total mass of 400 tons, that’s 10 KiloWatts delivered per satellite ton. I don’t know whether that’s economical, but it’s certainly possible to put into orbit.

To Do:

To pursue this option, several things must be researched.

1. The available metals must be evaluated for their behavior as plasma (especially containability) and their effectiveness as lasing materials. Typically, the pumping energy is somewhat higher than the output photon energy, and the pumping energy shouldn’t be higher than blue light, yellow would be better. The laser output color should probably be orange or yellow, depending on the capacities of the receiving PV systems. A metal must be selected, ideally matched to the band gap of the PV cells to be used.

2. Plasma containment technology must be investigated and a proposed design developed. Leakage must be estimated, as well as power requirements for the magnetic field(s) involved. I suppose superconductive magnets could be considered, although keeping them cold under those circumstances would probably require more energy (and weight) than using aluminum.

3. A mirror technology must be selected and a design created. Although I’ve been assuming a parabolic cylinder, with a 15 meter plasma beam a set of flat stretched film mirrors several meters across would be sufficient, if they were lighter.

4. All the final designs must be created with the launch considerations in mind, as well as the effects of cosmic radiation in GEO.

Hopefully, this will get the design onto the table for consideration. It needs a good deal of expert help, especially regarding the laser design, which is not the sort normally used today.

Alienthesaid

I have been slightly involved with copper vapour lasers and these are more temperamental and unforgiving than an opera diva. Maintenance is frequent and complicated, and the slightest mistake in powering up or down will cause destruction of the equipment.

Why not instead try Argon ion lasers? Again Pentagon has plenty of experiences in extreme high power use, supposedly for direct communications with submerged submarines as the blue/green light

@Neil Cox #71

The sun not being a point source is an interesting issue. I have looked up in my old optics books but these don’t cover anything more fancy than two lens geometric optics. I had hoped the use of 2 or 3 mirrors would do the trick but I am unsure. I would like to hear from someone experienced in optical design. If not there is always the possibility of using sunlight pumped parametric amplifiers.

Neil Coxsaid

I was thinking solar synchronous required about 20,000 kilometers altitude, but the following seems to say semi polar can be solar sychronous as low as 400 kilometers. The advantages of solar sychronous are the energy can be delivered during the peak demand period when it has a higher wholesale price, and several solar sychronous SSP can serve all the nations of Earth, during their peak demand period each day.
It’s called a “sun-synchronous” orbit, and it doesn’t quite follow the terminator.
The orbital plane of a satellite in low orbit will precess because of the gravity of the equatorial bulge of the planet it’s orbiting. If you choose the inclination of the orbit to the planet’s equator properly, you can get the orbit to precess at the same rate as the planet goes around the Sun.
For the Earth, the sun-synchronous inclination in LEO is around 98 degrees: a retrograde, near-polar orbit which will see permanently low sun angles if you set it up with an initial track near the terminator. Neil

Neil Coxsaid

The following from the forum at http://www.space.com may eventually be usable to build redirect antennas as suggested by Dan Lantz:
By bombarding the tip of a tapered optical fibre with ions, European scientists have succeeded in crafting a nano-antenna that operates at optical wavelengths and can efficiently ‘pick-up’ green light (Nano Lett. 7, 28–33; 2006). Such optical antennas may ultimately prove useful for subwavelength microscopy and integrated optoelectronic devices, but, for now, they show how a well-known object can be reduced to the nanoscale to create fascinating tools for the future.

Wireless technology literally surrounds us with information, and the concept of the antenna has a crucial role to play. By converting free-space electromagnetic fields into guided waves, or vice versa, antennas act as either receivers or transmitters. The wavelength at which antennas operate is intrinsically related to their size and shape: for a simple antenna, the height required is approximately one quarter of the wavelength.

For an antenna to operate in the optical regime, its dimensions must be on the 100-nm scale. This has now been achieved by scientists in Spain and The Netherlands.

Starting with the flat end of a single-mode optical fibre, Tim Taminiau and colleagues create a sharp glass tip by so-called heat-pulling — applying tension to hot, soft glass. This tip is coated with a 150-nm-thick layer of aluminium and is then shaped by bombarding it with high-velocity ions. The result is a nano-antenna that is just 50 nm in diameter and has a height of between 30 and 140 nm. By positioning it on the edge of an aperture into the optical fibre, the local field effectively drives the antenna, replacing the transmission lines in the radio-wave equivalent. Simulations of the fields around the structure show that it behaves in the same way as a standard radio-frequency monopole antenna, enhancing the localized field near the apex at a resonant wavelength dependent on the height: a 75-nm tall antenna is resonant with green light with a wavelength of 514 nm. The device could also act as a receiver when driven by far-field illumination.

To demonstrate the potential of their antenna, the team have used it to perform near-field scanning optical microscopy on fluorescent molecules suspended in a polymer film. Laser light at 514 nm is passed along the optical fibre to excite molecules and the fluorescence is collected in the same way. The sample is scanned beneath the antenna to produce a two-dimensional image and it is here that the effect of the antenna can be seen. The molecules can be resolved with a resolution of 26 nm, three times smaller than the patterns associated with the aperture. This result demonstrates the tight confinement of the enhanced field at the end of the antenna.

David Willardsaid

My background is at Intel Labs and semiconductor testing methods.
Here’s a tounge in cheek solution and provides buy-in to the naysayers and the “not in my backyard” issues.

Build the microwave receivers on the Nevada Test Site where the land is extremely polluted and cheap. Underneath put the Thorium reactors. Below the surface is the geothermal and hot rock stations for more power. Sprinkle the entire complex in solar panels to justify the costs and increase efficiencies. There’s a thousand square miles of desert there for the use

Power the robots to scrape the ground clean and put the waste and fallout into the Thorium reactor coolant and burn it up.
Power a 10 mile long rail gun and jettison the remaining nuclear vitrified ashes to ESCAPE orbit. Like 90 degrees to the ecliptic shot that never comes back. Use Magnesium Boron superconductors for the coils and contribute the shot energy onward to the grid.

The ground there is a total waste, and will get cleaned up. Nobody wants area 1-50, but they like to watch area 51 for space aliens. :}

It is possible to manufacture laser diodes with high efficiency like RAM chips on 8-10 ” wafers. IBM pioneered this technology back in 2000 or so. Billions of laser diodes possible with high yield and low cost, you betcha. Using semiconductor layering technologies and electron beam technologies, we can make lasers in several spectrums using the same substrate technologies.
Your ordinary DVD-ROM laser can be focused to light matches on fire. Can you imagine a cluster of 10000 on a wafer 10 mm and have been made to a spectrum mostly transparent to the atmosphere?

Like the gentleman in Iraq said, it’s a matter of willingness to pay for the energy. The US military is being shafted on a huge scale to get the oil they need at the right place and time.

It’s a matter on willingness, fear of pain of reduce supply and pretty much nothing gets done until there is a sufficient amount of overkill pain.

David Willardsaid

It’s a matter on mandate for energy security. When California was having rolling blackouts, the power should have came from a place like the Nevada Test Site. There should be an infrastructure requirement to carry that kind of capacity of electricity for the new hybrid cars just now coming on.

We have a so-called 90 day supply of oil, but no reserve capacity for electricity on our major grids? I remember the day the entire Pacific Inter-tie grid went down from a damned squirrel shorting out one substation here in Hillsboro Oregon. They fixed that problem AFTER all the nonsensical worries about Y2K. Yeah, the grid was good to survive rolling cascades of overloads and outages in case of plant failures or long line downage.

Lord help us if Al-Qaeda decide to attack the grid with more squirrels. They might even upgrade to explosives.

Roll it up in a plan for Homeland Security, they get a budget slice like the DOE and have some concrete examples to point at.

Neil Coxsaid

Most locals in the USA have about 5% reserve capacity above average peak demand. Much of California had a smaller reserve, which produced rolling blackouts whenever something went wrong during peak demand. Most of California’s problem was local residents did not want a new power plant built near where they lived.
The Soviet satellite illumination project would have produced about the brightness of Venus at it’s brightest, if my arithmetic is correct. Several satellites per city would be needed, to be significantly helpful. Hundreds of satellites bigger than 240 meters in diameter may be practical, as many cities use several percent of their total electric consumption for street and highway lighting. Neil

Neil Coxsaid

The size of the rectenna or light receiving site is mostly determined by how tight the beam can be made. The size of the illuminated spot is mostly determined by how long the beam is. From solar L1 (over a million miles) the illuminated spot might cover all of Texas. From a balloon ten kilometers away one square meter may be possible. In theory we can make the beam narrower by making the transmitting antenna or laser array bigger. The Arecibo radio telescope is the largest humans have built so far, for both transmitting and receiving. The last I heard they have a 445,000 watt transmitter that can send command signals to space probes up to about 50 billion kilometers away = 1/2% of a light year. We could say that space solar power has been demonstrated over huge distances, except nearly all the power missed the receiving antenna because the illuminated spot was much larger than the receiving antenna. Transmitting antennas up to 5 kilometers have been suggested for sending power 36,000 kilometers from GEO orbit. Likely that will work, but Arecibo is much smaller, so we may be surprised when we build a 5 kilometer or bigger transmitting array, especially as we will likely build it quite different from Arecibo. Sometimes things do not scale up as the math suggests.
A very high power density laser beam (or microwave beam) has additional spread because it is heating the air. I think HAARP found that the air heating effect was negligible even at ten million watts or more, but laser studies have shown considerable beam spreading due to the beam heating the air. Much of the data is secret, but Department of Defence is seriously considering space solar power, so they can likely access the secret data produced by HAARP http://www.spacesolarpower.wordpress.com. Another concern is the effect of the beam on humans and other life forms. Typically we have erred on the side of caution. Casualties and sickness from intense beams of electromagnetic radiation (radio to light) have rarely been documented other than the damage from radio heating as in diathermy. Above light frequency ionizing radiation, as in sun burn and gamma are well known dangers, but I have not heard any proposals to use these very short wave lengths for space solar power other than in science fiction. We do have to avoid human exposure to high density electromagnetic beams, but there is little evidence to suggest that 1/10 watt per square centimeter is dangerous, below the ionizing frequencies of ultraviolet light. Neil

Space solar power (SSP) is gradually beginning to look practical. Enterprising SSP ventures, such as Solaren Corp. and Space Energy, Inc., are in the midst of developing initial projects to supply energy from space. Solaren Corp. of California has recently reached an agreement with Pacific Gas and Electric, a California utility, to supply 200 megawatts of energy beginning in 2016, while Space Energy, Inc., a Swiss based company, is producing a prototype demonstration satellite that will help it close purchase power agreements with entities it is currently in discussions with.
As SSP advocates are painfully aware, the high expense of launching numerous payloads into space for the assembly of satellites large enough to transmit meaningful amounts of energy to Earth is cost prohibitive. While very large structures in space are theoretically within the realm of the technically possible for legitimate SSP interests, the launch costs associated with the construction of a satellite a few kilometers in length, as would be necessary for large scale energy transmission, are exorbitant. Additionally, the expense of space systems and operations—robotic technologies and the supporting space and Earth-based infrastructure—are extremely high and must be dramatically reduced. While proponents hope that large-scale space infrastructure projects will achieve certain economies of scale that will bring down the cost of each individual launch, component, and support system, the prevailing price tag for the whole of such a project would doubtless be enormous, making it very difficult to compete in the broader energy marketplace.
As such is the case, a critically sought after breakthrough may not be in space construction techniques or in PV performance, but rather in the nature of the physical composition of photovoltaic cells. If photovoltaic cells were produced with elastic properties affording them the capability of expanding, then a significant opportunity would arise for a novel new architecture for SSP: an inflatable sphere.

Scientists at the Technion – Israel Institute of Technology have already made certain strides in spherical photovoltaic technology with the development of photovoltaic balloons. While the Israeli development is of terrestrial photovoltaic balloon technology, the basic premise of crafting an inflatable sphere with elastic photovoltaic cells capable of expanding in reaction to the pressure of gases is a novel approach that could be a game-changing solution for cost-to-orbit factors and issues of on-orbit assembly that are necessary to resolve before establishing SSP architectures in space.

Indeed, the concept of an inflatable photovoltaic sphere is a simple idea that could possibly overcome many of the obstacles that SSP faces. As basic math bears out, such a design would enable extremely large satellites to be lofted into space with substantially increased surface areas. For example, whereas a satellite 5 kilometers in length and 2 kilometers in width would provide a surface area of only 10 square kilometers and would have to maneuver so that its photovoltaic cells could remain in the Sun, a sphere inflated to a diameter of 5 kilometers would provide an illuminated surface area of over 39 square kilometers with no orbital maneuvers necessary. Such architecture would be a far more ideal for damming the nearly 1.4 gigawatts of solar energy continuously pouring through every square kilometer of space in Earth orbit.

The key to the concept’s feasibility is the ability to inflate the sphere rather than painstakingly assemble it in orbit. The sphere could of course be condensed into a very small package for transport into space and would then expand once it achieved orbit. The use of gases would be critical in this regard—large amounts would be compressed very tightly, would weigh virtually nothing, would cost very little. Such a system would still face major technical challenges, including maintaining integrity in a space environment filled with micrometeorites and space debris.

According to the 2007 National Security Space Office (NSSO) study on SSP the United States has limited capabilities to build large structures in space and cannot at present move large amounts of mass into orbit. The United States correspondingly has extremely limited capabilities for in-space manufacturing and construction or in situ space resource utilization. By crafting a balloon-like satellite the amount of on orbit construction for SSP infrastructure would at once be drastically reduced in tandem with the amount of launches necessary for establishing this architecture in space. In wholesale fashion the inflatable sphere would eliminate the many structural components that conventional SSP spacecraft possess, mooting many questions of modularity maximization in the process.

The spherical concept would enable cost-to-orbit factors to be lowered considerably as the platform would weigh much less than conventional models and would require far fewer launches to be brought online. Whereas other SSP plans call for slashing the cost per pound to orbit with substantial increases in launches, the inflatable sphere would slash the overall launch costs by lessening the amount of launches required while still producing a massive surface area for the production of solar energy.

While it would be highly desirable to possess the capabilities discussed in the 2007 NSSO study, an inflatable sphere would be a design that could by-pass the necessity of their development in the short term, making SSP technically and financially practical in the immediate future. Perhaps the resources engendered from the success of spherical SSP could then in turn be utilized to advance the aforementioned capabilities for other commercial, scientific, or military endeavors in the medium of space.

However, for large systems, pieces of the sphere would have to be sewn together in orbit before it can be inflated. If this were the case, larger spheres would doubtless face similar technical obstacles as the smaller conventional SSP platforms in that a significant amount of launches and on orbit assembly would be required for both. It would therefore be necessary to develop the capabilities previously mentioned in the 2007 NSSO SSP study before the project could be undertaken.

Nonetheless, the spherical design would nevertheless continue to afford a satellite with a far larger surface area producing far more solar energy for the amount of resources that were invested. Once an extremely large sphere—100 kilometers in diameter—had been crafted in space, it could be inflated to its full size and would then have the potential of producing tens or hundreds of terawatts of energy from an illuminated area in excess of 15,700 square kilometers. By comparison, the alternative designs, which would also require numerous launches and on orbit assembly, would only produce gigawatts. With the ability to produce such vast amounts of energy, large-scale spheres would surely overcome the manifold economic barriers that have thus far thwarted SSP endeavors, justifying the incursion of the full spectrum of costs—launch, in space assembly, supporting space systems, and supporting terrestrial infrastructure.

Indeed, inflatable space-based spheres with elastic photovoltaic cells could be the energy technology breakthrough that much of the world has been waiting for. Should a space-faring nation with the requisite resources proceed to ring the Earth in GEO with relatively small photovoltaic spheres, or if it should fashion giant photovoltaic spheres, or if it should proceed to do both, the energy resources that the nation in question will have availed itself would be more than considerable. A nation such as the United States would have developed enough clean and renewable solar energy to become one of the world’s foremost energy exporters.

If solar power satellites such as these did come into being, they would very likely necessitate the overhaul of the entire global economy to achieve broad compatibility with the new energy technology. The resultant economic transformation would be incredible, creating many new high technology jobs in industries across the world, but especially in the nation that was at the epicenter of the SSP breakthrough. In fact, of greatest economic impact may not be the new energy technology itself, but rather the wave of innovation arising in complement to the new energy technology.

And yet the tremendous symbolic power that these satellites could possess may have a profound impact far beyond the realm of economics and the environment. Due to their photovoltaic properties, large enough spheres could have a crystalline appearance in space visible from the Earth with the naked eye, giving them the appearance of diamonds in the sky. If this were the case, these satellites would not only drastically reduce carbon emissions and provide a plentiful source of renewable energy, but there physical beauty across the backdrop of both day and night skies could be surreal for onlookers, causing many around the world to become enamored with the entrepreneurial verve of a nation that developed them as well as with the culture that created them. A nation that owned and operated what appeared to be diamonds in the sky producing abundant clean energy would surely be at the forefront of global leadership, attracting the sentiments of much of the world’s population into its socio-political camp.

Of even greater socio-cultural impact could be their effect on the technological aptitude of a nation, as the case may very well be that crystalline discs shining like diamonds in the sky could inspire an entire generation of young Americans to excel in math and science like never before. With the tangible, ever present symbol of mathematical excellence glimmering in the sky by day and by night, kids could very likely develop a whole new appreciation for the “coolness” of science.

Trevor Brown is an author focused on political, economic, and military strategy for the medium of space. He holds a BA from Indiana University and an MSc from Nanyang Technological University.pmn1 e » Fri Jun 05, 2009 5:41 pm

Interesting concept…but instead of pressurizing the balloons, why not use electric charge to “inflate” the balloons? There are several advantages to this:

1.) In the event of a micrometeorite impact, it would simply pass straight through the balloon while perhaps knocking out a small, insignificant piece of the balloon without causing a violent depressurization which would cause significantly more damage.

2.) In the event of a tear due to an impact, a similar charging mechanism could be used to bring adjacent cells together and some static bond could “re-seal” the structure…however, this may not even be necessary; consider Christmas tree lights which are connected in parallel, if one light goes out the rest function fine, unlike series connected lights.

3.) To state the obvious, you wouldn’t need to pay for gas

» Fri Jun 05, 2009 5:43 pm

In fact…you may not even need to repair any missing parts unless the part knocked out was sufficiently large enough to cause a huge drop in power…after all, what are a few solar wind particles going to do to it if they get inside
e
~by neilsox » Sun Jun 07, 2009 8:45 pm PDT
The electric charge to inflate the balloon in orbit (after or instead of inflating with hydrogen) may make the idea doable. If the balloon has a total surface area of 10 square kilometers and a total mass of one million kilograms = 100,000 kilograms per square kilometer = 100 grams per square meter. Much of that mass would need to be the electrical conductors that connect the flexible PV in series parallel, otherwise resistance losses will be excessive. Possible as the balloon needs very little strength in LEO = low Earth orbit and in theory the stretchable PV cells can be extremely thin. You may have a winner. Proven in LEO, similar balloons may be practical at GEO altitude = 36,000 kilometers. Neil~

Andrew Blosssaid

I think the Dark Sky balloons go well with SBSP. The balloon based power stations can also be receivers at night for space based powers. So there is no land footprint, apart from the tether, and the power supply is not interrupted by night.

As an aside, could the balloons themselves store power for the night? Split water during the day and store the hydrogen in the balloons and burn it at night.

And finally, perhaps you can reduce launch costs by building an electric space plane with power cells on the wings.

Neil Coxsaid

Hi Andrew; We do loose some energy each time we change the voltage or type of energy, but perhaps your idea has merit. My guess is suitable lasers will be available for SSP soon. Carbon fiber tethers are lighter. Carbon fibers can make the hydrogen gas envelope lighter. Thin film PV = photovoltaic promises about 15% efficiency at much more watts per pound of weight, so we might have a 1/2 square kilometer solar receiving site sharing the top of 3 hydrogen filled balloons each almost 1/2 kilometer in diameter. Three tethers to the ground carrying 3 phase ac connected directly to the grid. 26,140 feet = 5 miles may be practical as several tethered balloons have operated for many years at 15,000 feet. The record for untethered balloons is about 150,000 feet, but that is free flying, negligible payload, which does not get the energy to the ground. The tethers are heavy to carry 100 megawatts almost 30,000 feet.
When the sun is almost overhead, 10 megawatts might be delivered to the grid, jumping to 100 megawatts when a beam is available from an SSP = space solar power. Higher beam density, likely requires the thin film PV to be hydrogen cooled. This does however warm the hydrogen perhaps enough to avoid lower altitude due to the extra weight of the cooling system. 100 megawatts per 1/2 square kilometer = 200 watts per square meter = about average sunlight intensity, except we need to divide by 0.15 = 1333 watts per square meter. Think 2000 watts per square meter as there are losses in the inverters and the three tethers which are almost 30,000 feet long. 2000 watts per square meter of laser light will produce heat exhaustion and/or sun stroke in humans in minutes on a very hot day, if the human is unable to find shelter. Likely not at all harmful in cool weather. The beam from the SPS can shutdown in less than one second if a balloon or surface solar site is not receiving the beam, so injury is very improbable. Lightning strikes on the tethers are however a problem. 100 megawatts is a about 50 amps per tether at one million volts. Likely somewhat less than one million volts will be the optimum design. If a bipolar HVDC power line is being fed the numbers come out slightly better. See HVDC in wikipedia for what appears to be accurate details about HVDC. Gas turbines burning hydrogen in the thin air at an altitude of 5 miles are too heavy to be practical in my opinion. Recycling the water from the hot flue gas and electrolyzing it also adds a lot of weight. Neil

Kurtsaid

About addressing the power beam laser’s damaging anything the flew through them, would it be possible to exert the microwave energy in a non concentrated way (no lasers) and once they reach the elevator have them be concentrated to power the elevator? The same principle behind capturing solar energy more efficiently, where sunlight was used by concave mirrors to reflect sunlight into solar cells but due to the concave mirrors the energy was much more concentrated. Any thoughts?

Neil coxsaid

Hi Kurt: Except at a gigawatt or more, I don’t think it is presently possible to produce a microwave beam that is dangerous at a range of 1000 kilometers or more. I agree dangerous is necessary for the climber on a space elevator or bolo = short rotovator. Lasers can produce high energy density = dangerous at the climber receiving disks at ranges up to at least 36,000 kilometers. The enroute danger can be reduced considerably by using widely spaced multiple lasers to illuminate the receiving disks on the climbers. Multiple lasers at various locations are needed anyway as I belive the climber will rotate slowly on the ribbon of the elevator or bolo, as the ribbon rotates. I don’t think it will be practical to prevent the ribbon from rotating = twisting. Neil

Chris Radcliffesaid

I would like to reference your paper entitled “Sun-Powered Laser Beaming from Space for Electricity on Earth” for a Sustainable Energy Class that I am taking at the University of Utah. I am doing a general paper or Space Based Solar Energy. Let me know if you are okay with this. Thanks for you information.

Neil Coxsaid

I did not write that paper, but you have permission to use any of the material I have posted on this forum. Laser beaming is possible with presently available equipment, but system cost is perhaps more costly than microwaves. Cost is the result of low laser power, for light weight diode lasers. Other lasers are presently too heavy and temperamental. Several outfits are working on multiple lasers that are phase locked, but last I heard, such is not yet available. The alternative is separate optics for each laser, which adds considerable weight and cost. The main difference between lasers and microwaves is small scale demonstration units are practical for lasers, but large scale laser systems present a hazard to humans, as a concentrated beam is possible with lasers, but not with microwaves. A very concentrated beam makes the receiving site on Earth’s surface much smaller and thus less costly. Better, the solar = laser receiving sites already are operational around the world, but receiving sites for microwaves have to be designed and built a mile or more in diameter each. Dedicated receiving sites for specific laser frequencies will be twice as efficient as the present solar sites, but half is adequate for demonstration purposes. Microwave receiving sites will also be frequency critical and not readily modified for a different microwave frequencies. Neil

Neil coxsaid

SPS = solar power satellite. SBSP = Space based solar power. SSPS = ? An early satellite will have a 2000 square meter solar panel. Perhaps 20 million solar cells in series to produce 10 million volts at 1/10 amp = one million watts. The low current means low copper loss, even if we use #26 wire. For best results the panel must turn to face the sun. That should be comparatively easy. Thermal couples mounted on the back of the cells can provide auxiliary power for the satellite electronics and miscellaneous. The panel will be optimised for watts per kilogram, and long life in space rather than watts per square meter or efficiency, so the about 40% efficiency may be optimistic. The transmitting antenna needs to point at a single square kilometer on Earth’s surface, so extreme precision is needed to keep the beam that narrow and centered on the rectenna on Earth’s surface. Even using 10,000 megahertz (3 centimeter wavelength) The transmitting antenna is bigger than the solar panel. Likely much bigger from 36,000 kilometers away = GEO altitude. We should seriously consider solar synchronous semi polar orbits for the early satellites to reduce the altitude, make the energy available, occasionally to all the nations of Earth and permit a much smaller transmitting antenna, with less energy spilled outside the rectenna. A dozen such satellites can supply power to all the nations (who build a rectenna) every evening during the peak electricity demand period when electricity is worth up to 50 cents per kilowatt hour. Electricity is worth much less during most of the rest of the day and night. So far we have one megawatt at the solar cells. 990 kilowatts at the input to the 99 klystrons in series running off the almost ten million volts. Klystrons are good as they can be modulated with wide band data which may be far more valuable than the electricity. Most locations on earth and through out the inner solar system will be able to receive the data due to several kilowatts which is scattered from the beam by earth’s atmosphere and imperfections in the transmitting antenna. I’m guessing the rectenna will produce 1/2 megawatt of low voltage direct current. perhaps 400 kilowatts that goes on the grid as high voltage 60 hertz 3 phase electricity or million volt HVDC = high voltage direct current. Is there any practical way to connect ten million dipole rectifiers in series so we can avoid another energy transformation which loses several more percent?
I suggest a flexible power line tethering the transmitter and antenna satellite to the giant solar panel, thus allowing both to aim independently. Concentrating mirrors can be added later to boost the beam power by perhaps ten times. The thermocouple units will then become active cooling devices to prevent heat damage to the solar cells. The ten million volts will no longer be optional when a 1000 amp solar panel is built in space = ten gigawatts at ten million volts. Most of the above is applicable if we use millions of laser diodes instead of klystrons or magnetron’s. Neil

Neil coxsaid

We need to pursue all promising alternative energy sources faster than seems prudent except nuclear which has extreme down side if we fast track. The main objection to thorium nuclear reactors is even massive funding would require more than a decade to get to the second gigawatt except at high risk. This is especially true as powerful people want thorium to fail.
If the properties of liquid nitrogen super conductors can be optimised, they are likely practical for long distant power lines. Near term, HVDC = high voltage direct current power lines are operational and superior to 60 hertz three phase power lines for up to about 1500 kilometers. We could build a town that uses dc instead of ac appliances, as avoiding the conversion back to ac may reduce losses if not improve cost effective. Can dc wind turbines be operated in series to produce a million volts dc? Likely, but it may be impractical for several reasons. Yes, electric vehicles can help stabilize a dc grid, but the concept is not well established for ac nor for very high voltage dc. The cost is unknown and vehicle owners who decide at the last minute to take a trip will be unhappy, if the grid just halved the range of their vehicle. This will upset most consumers even if it happens rarely.
For SBSP = space based solar power, I like sun synchronous orbit as the satellite can stay over the sunshine terminator, and thus be able to beam power approximately straight down to cities that are experiencing peak demand. (Ten degrees above the horizon, in all possible directions means the rectenna must have lots more area than for a beam coming from directly above) Early evening is when the power is worth up to 25 times the midnight price. Other advantages are the satellite is at lower than GEO orbit so the aiming is less critical and the transmitting array can be smaller and all the nations of Earth can be served at least rarely by a single solar synchronous satellite in a semi polar orbit. About 12 satellites are needed to provide hundreds of rectennas every late afternoon and every early evening.
Lasers may be available soon as an alternative to micro waves. Existing solar sites can receive, up to several megawatts of laser energy, as small as 4000 square meters = a 64 meter square, while rectennas need to be much larger because microwaves illuminate a larger spot. A receiving site dedicated to the transmitted frequency/wave length will be about twice as efficient, but we can tolerate reduced efficiency for demonstration purposes. Neil

Raymond N. Coxsaid

Ore similar to regloth can be purchased for a few dollars per ton in many places on Earth, but we don’t extract silicon or aluminum from this ore, likely because expensive ore is less costly to extract the elements from. Perhaps we can learn how to extract elements from regloth and cheap earthly ore that is competitive with the expensive ore, but costly research and development is needed.
From GEO altitude the plan was a kilometer antenna that sent a billion watts to a rectenna with an area of about 20 square kilometers. Since the moon is about 10 times farther away, the area of the rectenna increases to about 100 times that area = 2000 square kilometers. In theory we can send 100 billion watts with the same energy density just above the rectenna. Not even New York City needs that much power, so we have to add the cost of thousands of kilometers of HVDC = high voltage direct current power lines, or less efficient 3 phase 60 hertz power lines to take the power to customers. We can cut corners and make the rectenna smaller, but most of the energy misses the rectenna, which makes the people living near the rectenna fearful even though they are not harmed by the exposure to the micro wave energy, according to most experts. We can transmit with lasers on the moon and ordinary solar panels and solar thermal systems can receive the energy, but the laser technology isn’t there yet = maybe in ten years. So one problem is even a demonstration system from the moon is incredibly costly. Investors are wise to be skeptical if the scale up is one million times from 1000 watts (demonstration) to one billion watts delivered to the grid.
To me it seems a semi polar sun synchronous orbit (closer than GEO) is the way to go, as it could provide electricity to all the nations of Earth during their peak demand period. There are lots of related details in the forum at http://www.spacesolarpower.wordpress.com Hurry, the forum could be deleted soon, as they are not approving new posts this year. Neil

Neil Coxsaid

~87 weeks ago at change.org No new posts. My comments are enclosed with~

This response is filed on behalf of the National Radio Astronomy Observatory, headquartered in Charlottesville, VA. NRAO (http://www.nrao.edu)is a federally-chartered facility funded by the National Science Foundation for the purpose of constructing and operating radio telescopes in the pursuit of radio astronomy world-wide. Owing to a capital investment of over $1,000,000,000 in state of the art radio frequency astronomical instruments such as the eVLA, VLBA, Robert C. Byrd Green Bank Telescope and ALMA, NRAO and its user community are major stakeholders in the electromagnetic spectrum. They stand to be seriously impacted by testing, development and/or implementation of space-based solar power satellites (SPS) for terrestrial power generation. ~Some impact will occur, but they can find solutions until the SPS total is many gigawatts. By then, present equipment will be obsolete and the far side of the moon may be the main radio astronomy location which will not be impacted by even 1000 gigawatts of SPS~ The ill effects of SPS are hardly limited to astronomy nor have they lessened with the passage of time.

To capture and repackage as microwaves the same solar radiation which naturally falls on earth as sunlight, SPS would place huge (~75 sq km) solar collectors and multi-gigawatt rf transmitting systems into the heart of the geosynchronous satellite belt. Even in normal operation the presence of these transmitters could wreak havoc on other spectrum users (astronomy, terrestrial-satellite links and the like) because, with the inevitable leakage of even tiny fractions of gigawatt peak levels, it is impossible ~solutions will be possible in most cases~ to prevent interference across a broad swath of the spectrum. Moreover, generation of gigawatt power levels using literally millions of individual kilowatt power sources per SPS station will involve large amounts of spurious noise as the individual elements fail; even for a mean lifetime of 30 years, dozens of elements will fail each day at each station in high, geostationary orbit where servicing is extremely difficult. And even optical and infrared astronomy will not be immune because the SPS collectors will light up the sky at optical and infrared wavelengths day and night owing to reflection and heating of the solar panels. ~even 1000 gigawatts will be minor compared to the present light polution, cities world wide produce~

SPS systems have other liabilities. On the ground, they also require huge land preserves harboring rectifying antennas whose areas are comparable to what would be required to generate gigawatts of power from incoming solar power directly. The mean power levels beamed to earth as microwaves across these ground antennas by SPS are comparable to those of normal incident sunlight, but as microwaves they are well above human safety levels. ~True for the present standard of 0.1 watt per square centimeter, but considerably higher microwave energy levels are tolerated by humans at most frequencies, except on extremely hot days~ The need for such elaborate, remotely-sited ground receiving stations precludes use of SPS in case of sudden emergencies; it cannot be beamed wherever it might be needed. ~Some casualties from the beam is likely acceptable, if the energy allows the saving of many other lives~

It is a separate decision whether to entrust the national power supply to SPS ~1% is not entrusting/when and if we reach 1% we can consider if further scale up is prudent~ with it’s ~not~ obvious vulnerabilities. The vast amounts of rocketry needed may cause other bad side effects. NRAO recommends that the pursuit of SPS systems for terrestrial power generation should be abandoned, as the potential harm ~possibly~ outweighs the benefits. NRAO urges that the solar power research effort be turned toward development of appropriate technologies (such as power storage) which would allow ground-based solar collectors to be ~possibly~ adequate as a source of electric power. If development of SPS for terrestrial power generation proceeds, NRAO asks that the interests of all spectrum stakeholders be protected. ~using laser frequencies (instead of microwave) reduces most of these problems significantly. Neil~